The overall objective of the program is a detailed study of congenital abnormalities of the visual pathways that occur in a number of different mammalian species including the human. Animals lacking pigment in the retinal pigment epithelium develop abnormal retinofugal pathways. The developemnt of the earliest retinofugal axons is being studied between the eye cup and the optic chiasm, and special attention is being paid to situations in which the axons may relate to pigmented cells. The structure of the optic chiasm and of the post-chiasmatic pathways is being studied in abnormal cats and mice. The development of the abnormal pathways within the brain is also being studied in cats, mink and ferrets in order to determine when the abnormality first appears and to demonstrate how the development of the abnormal pathways relates to, perhaps even produces, secondary cerebral abnormalities within the visual relays.